Functions of electrophotographic image forming apparatus are to uniformly charge a photosensitive drum, imagewise expose the photosensitive drum to an original pattern light to make the drum discharge on the exposed area to form an electrostatic latent image, adhere a toner to the latent image, and electrostatically transfer the adhered toner to copying paper.
The image forming apparatus has a developing roller at the opening of a toner cartridge so as to face to a photosensitive drum.
In conventional apparatus, the parts of a toner cartridge where the developing roller are held are covered with felt.
On the other hand, known sealing materials which are used in contact with a photosensitive drum to prevent toner leakage from the drum include an elastic material laminated with a 20 to 200 .mu.m thick heat-shrunk fluorine resin film as proposed in JP-A-U-60-16154 (the term "JP-A-U" as used herein means an "unexamined published Japanese utility model application") and an elastic material laminated with a 30 .mu.m thick heat-shrunk fluorine resin film as proposed in JP-A-U-60-173960.
When felt is used at the roller holding parts of a toner cartridge, the felt is battered through long-term use to make a gap between the developing roller and the holding parts. As a result, a toner is leaked therethrough or passes through the felt fibers to contaminate the inside of the apparatus or to stain copies, causing poor image quality.
Further, when the sealing material disclosed in JP-A-U-60-16154 or JP-A-U-60-173960 is applied to the roller holding parts of a toner cartridge, there sometimes results the following disadvantage.
The surface of bearing parts of a developing roller sometimes has unevenness in the axial direction due to the surface finishing. In particular, if there is a protrusion, the elastic material undergoes great deformation via the fluorine resin film in contact with such a protrusion to cause stress concentration. As a result, the fluorine resin film is broken or worn out or does not fit the developing roller. This being the case, a gap is formed between the sealing material and the roller, and the toner leaks therethrough to contaminate the inside of the apparatus or to stain copies.